1. Field of the Invention
The present invention relates to a gallium nitride group compound semiconductor light-emitting device and a method for producing the same. More particularly, the present invention relates to a gallium nitride group compound semiconductor light-emitting device, which is preferable as a gallium nitride group compound semiconductor laser and a gallium nitride group compound semiconductor light-emitting diode, capable of emitting light from the blue region to the ultraviolet region of the spectrum; and a method for producing the same.
2. Description of the Related Art
FIG. 7 shows one example of a conventional compound semiconductor laser device. This compound semiconductor laser device is an InGaAlP group compound semiconductor laser having an internal current blocking layer. Such a semiconductor laser is disclosed in, for example, Japanese Laid-Open Publication No. 62-200786.
The structure of this semiconductor laser will now be described together with a production method thereof. First, an N-type GaAs buffer layer 201, an N-type InGaP buffer layer 202, and an N-type InGaAlP cladding layer 203 are formed in this order on an N-type GaAs substrate 200 in a metal organic chemical vapor deposition (MOCVD) apparatus. Then, an InGaP active layer 204 is formed on the n-type InGaAlP cladding layer 203.
Next, a P-type InGaAlP cladding layer 205 (205a and 205b) including an etching stopper layer 205', a P-type InGaAlP contact layer 206 and a P-type GaAs contact layer 207 are formed on the InGaP active layer 204.
Then, an N-type GaAs current blocking layer 208 and a P-type GaAs contact layer 207 (207a and 207b) are sequentially formed. Thereafter, a P-side electrode 209 and an N-side electrode 210 are formed. In this manner, the InGaAlP group compound semiconductor laser device having a waveguide structure and an internal current blocking layer is completed.
This type of InGaAlP group compound semiconductor laser device has the following problems due to the production method thereof.
More specifically, the method for producing this type of semiconductor laser device requires, during the production process (i.e., after the contact layer 206 has been formed), the steps of taking out the N-type GaAs substrate 200 having semiconductor layers stacked thereon (i.e., wafer) from the MOCVD apparatus; etching the P-type InGaAlP cladding layer 205 by wet etching or dry etching to form a stripe-shaped projection; placing the wafer with a surface of the P-type InGaAlP cladding layer 205 being exposed again in the MOCVD apparatus; and regrowing the N-type GaAs current blocking layer 208 on a portion of the exposed surface of the InGaAlP cladding layer 205. In the regrowth step, a substrate temperature needs to be raised to about 700.degree. C.
As a result, during a rise in the substrate temperature, surface roughness at the exposed surface of the P-type InGaAlP cladding layer 205 is increased. Moreover, the width W of the striped-shaped projection as well as the distance t between the N-type GaAs current blocking layer 208 and the InGaP active layer 204 are changed.
Consequently, in a compound semiconductor laser having such a structure as described above, the crystallinity of the regrown internal current blocking layer is deteriorated. Moreover, both the width W of the stripe-shaped projection and the distance t between the current blocking layer and the active layer are changed, as described above. Thus, electrical and optical characteristics of the semiconductor laser are deteriorated, making the semiconductor laser less reliable.
The above-described problems occur also in a gallium nitride group compound semiconductor light-emitting device.